In magnetic resonance tomography (“MRT,” also known as “MR”), high-frequency coils (hereinafter interchangeably called “local coils”) are used for receiving alternating magnetic fields. The local coils are sensitive to alternating magnetic fields and have one or more antenna elements with a copper conductor. The individual antenna elements may be embodied as annular loops, (e.g. as loop antennas (“loops”)), butterfly-coils, or saddle coils.
In addition to the at least one antenna element, a local coil also may have at least one preamplifier and further electronic devices (RF chokes, etc.). The further electronic devices may include cabling, a housing and one cable with a plug, connecting the local coil to an MRT unit or MRT system. A receiver connected on the system side filters and digitizes the signal received from the local coil and transfers the data to digital signal processing. An image or a spectrum may be derived from the measurement. The derived data may be provided to a user for diagnosis.
In order to obtain a particularly good signal-to-noise ratio, the RF coils are adjusted, with regard to the geometry and receive profile of the RF coils, to different areas of the body and positioned as close as possible to the patient's body. For example, the RF coils may be positioned on the patient (anterior) or under the patient (posterior). The local coils may geometrically cover the area to be investigated as precisely as possible. For example, the local coils may have a larger geometric size for a larger patient and a smaller geometric size for a narrower patient. Conventional local coils are accommodated in a rigid housing or in a plastic casing. Conventional local coils may be flexible but not expandable.
DE 10 2010 033 322 A1 discloses a mechanically flexible MR coil with opening conductor structures for interventional magnetic resonance tomography. The disclosed local coil for a magnetic resonance tomography system has at least one antenna element, with at least one antenna element having a detachable connection to form an opening.
DE 10 2012 200 599 A1 discloses an antenna system for a magnetic resonance imaging system with multiple antenna elements. The antenna elements are arranged in, at, or on support elements. The support elements are not constructed to be expandable and have a constant surface dimension. Adjacent support elements are connected via an expandable connecting element, whereby the dimensions of the connecting element may be changed as a result of expansion.
DE 100 51 155 A discloses a reception coil arrangement for nuclear spin tomography systems with a plurality of selectively pluggable local coils. The local coils with active detuning have a passive detuning circuit for the transmission phase and a passive detuning circuit for the reception phase in the unplugged state. A detuning resonant circuit includes a detuning coil and a capacitor in series with a reverse biased diode that becomes conducting when the coil is connected to the extraction RF cable of the local coil. The detuning coil is dimensioned to form a high-impedance parallel circuit with the matching capacitances of the RF antenna tap, between the terminals thereof.